In situ XAFS study on Mo oxide catalysts by molten salt preparation
Résumé
Prepn. of catalysts in molten salt has great possibilities for producing excellent catalysts because the reaction in molten salt is quite different from that in water. MoO3 dissolves in molten salt and finally becomes molybdate via intermediate oxoanions as catalytic active species. The structure of the oxoanions and the mechanism of stabilization on zirconia in the prepn. process remain unknown. In the previous study, we have clarified the changes in the compn. of molybdate species during the catalyst prepn. procedures by quenching the samples. In the present paper, the structure of Mo oxoanions in molten nitrates at different temps. was investigated by in situ XAFS. Samples were prepd. from MoO3 in molten nitrate (NaNO3). The mixt. was heated up to various temps. from 298 to 773 K. The in situ XAFS spectra of the molted samples were measured on Mo K-edge using an in situ cell at the BL-10B in the Photon Factory. The EXAFS was analyzed quant. to obtain the structure and compn. of Mo oxoanions in the molten nitrates by multi-component fitting based on a linear combination of chi(k) of ref. samples and simulation using FEFF8 code in consideration of the Debye-Waller factor. The results show a change of compn. of oxoanions in molten nitrate during the reaction.